The invention herein relates to a simplified and safe diagnostic method and assembly for the rapid determination of ligands or antiligands which does not require special skills to perform.
There are a number of immunological methods which have been developed for the determination of a wide variety of ligands and antiligands. Generally such methods rely upon the interaction between an antigen and its antibody. Such methods provide a label to one of the components of the antigen antibody pair such that when the labeled component is introduced to a sample containing the unknown corresponding antigen or antibody for the labeled component, a reaction occurs which can be monitored by use of the label.
Antibodies or receptors have been utilized for many years in a wide variety of procedures for detecting or measuring antigens or ligands. In many of such techniques, results can be determined by simply measuring the signal produced from the antibody-antigen reaction. For example, some techniques provide an agglutination or precipitation upon reaction forming the antibody-antigen complex. However, many antibody-antigen reactions doe not readily produce measurable signals and it is often necessary to label one or the other component of the reaction and monitor the signal produced by that label.
Labeling of one of the components can be accomplished using various techniques. In the 1960's and 1970's, a commonly used label for the components consisted of the use of radioactive isotope. More recently, nonisotope labels such an enzyme, chemiluminescent, and fluorescent labels have been found to be more convenient and safe. Such labels have, therefore, gained in popularity.
Even with the advent of nonisotopic techniques, performance of immunoassays still requires highly skilled persons and relatively sophisticated laboratory equipment. With the changing economic environment, there is a need for safe, accurate, rapid, and relatively inexpensive immunoassay systems which are sufficiently simplified for nonlaboratory persons to perform in environments such as a doctor's office, a patient's bedside, satellite laboratory, or home environments. Unlike currently available laboratory procedures, methods intended for use by less skilled persons must also be designed to minimize the risk of spreading infectious disease agents potentially present in test samples.
Immunological methods can be categorized as competitive or noncompetitive binding assays and as heterogeneous or homogeneous assays. In competitive binding assays, an unknown ligand or antiligand and a similar predetermined component compete for binding sites on a binding partner. Either the binding partner or the competing component is labeled and the unknown is indirectly measured by determining the extent to which the labeled component is bound to the limited amount of binding partner. In noncompetitive binding assays, there is no added component that competes for the unknown's binding partner. The unknown is directly measured by determining the degree to which a labeled binding partner is bound directly or indirectly to the unknown.
The distinction between heterogeneous and homogeneous assays is based on whether a bound/free separation step is required. Homogeneous assays do not require physical separation of bound and free labeled components because results are based on the modulation of the label's signal when the labeled component is bound to its binding partner. Although the performance of homogeneous assays is relatively simple, they are less sensitive than heterogeneous assays and usually are limited to the measurement of smaller antigens. In addition, homogeneous assays require relatively expensive instrumentation to monitor the modulation of the label's signal.
Heterogeneous assays require physical separation to isolate bound labeled complex from free labeled component before results can be determined. Separation is generally accomplished by one of several methods including electrophoresis, filtration, adsorption, precipitation, and/or centrifugation. Because the separation step is a critical step in the procedure, performance has required either sophisticated, automated equipment or considerable care and precision on the part of a well trained technician.
An important consideration in working with heterogeneous assays is the potential for spread of infectious disease agents which can be present in the specimen being tested. At some time in the separation step, either a portion of the reaction mixture must be transferred to another vessel or free components are washed off a solid phase material. When such transfer or washing steps are performed manually, there is a considerable risk in contaminating surrounding areas or persons performing the procedures.
It would be desirable to provide an immunoassay with the broad application of heterogeneous assays which is also simple, rapid, accurate, and safe for unskilled persons to perform in environments outside of sophisticated laboratory settings, when single sample determinations are desired. Such an assay should be convenient and inexpensive, eliminate the need for critical washing steps, and reduce the risk of spreading infectious disease agents.